This invention relates to a fixing device for use in an image forming apparatus equipped with a temperature detecting device for accurately detecting the surface temperature of a heating roller as a fixing roller in the fixing device.
In a conventional technology, it has been adopted for a temperature detecting device for detecting in a non-contact way the surface temperature of the heating roller in a fixing device to control it, means for determining the temperature of a measurement object on the basis of the correlation between two sensors, a surface temperature detection sensor detecting the surface temperature of a heating roller mainly by radiation heat and a compensation temperature sensor detecting the ambient temperature mainly by the heat conduction in air; however, depending on the placement position of the two sensors, the detected temperature tends to be subject to the influence of convection and conduction, and it sometimes becomes impossible to detect accurately the true surface temperature of the measurement object, that is, the heating roller.
As regards such a temperature detecting device, means for measuring the temperature of a measurement object which eliminates the influence of the smudging of the sensors making up the temperature detecting device in cases where the smudging happens is described in the Japanese publication of the unexamined patent application 2001-034109. However, there is no reference in which means for detecting the surface temperature accurately and stably by specifying the positional relationship between the heating roller, the measurement object, and the temperature detecting device at its surface is described.
Further, this invention relates to an image forming apparatus such as a copying machine or a printer employing an electrophotographic method, and in particular, to an image forming apparatus equipped with a fixing device for fixing a toner image formed on the basis of image information on a recording material.
Heretofore, in an image forming apparatus such as a copying machine or a printer using an electrophotographic method, in order to fix a toner image formed on the basis of image information on a recording material such as a paper sheet, generally, a heat roller fixing method is used.
This heat roller fixing method is a method in which toner particles are fused by the heat of a fixing roller with its surface layer formed of a metal having a halogen heater as a heat source arranged inside and fixed on a recording material.
In fixing, if toner particles are fixed at temperatures not lower than a specified temperature, the toner particles adhere to the fixing roller, and in the case of fixing at temperatures not higher than a specified temperature, it becomes the cause of producing a noise called a fog, which degrades the image quality. Further, if toner particles are fixed at temperatures not higher than a specified temperature, it occurs a poor fixing phenomenon in which some toner particles are stripped off the recording material due to the friction against it.
Accordingly, in fixing, it is necessary to carry out temperature control through the detecting of the temperature of the fixing roller accurately in order that the temperature of the fixing roller may fall within a specified temperature range.
However, it sometimes happens an accident such that, for the purpose of detecting the temperature of a fixing roller, during fixing operation, when an operator, having an intention to measure the actual temperature (hereinafter referred to as the surface temperature) of the fixing roller by bringing a contact-type temperature sensor in contact with the surface of the fixing roller, brings the sensor into contact with the rotating fixing roller, the fixing roller is damaged, or an accident such that toner particles adheres to the temperature sensor and the adhering toner particles smudge a recording material.
Therefore, there has been a problem that, in order to prevent such an accident, if the surface temperature of a fixing roller is measured by means of a non-contact type temperature sensor, because the fixing roller is distant from the non-contact type temperature sensor, which is subject to the influence of the temperature of the environment in which the fixing roller is placed, for example, the temperature of the machine parts inside the image forming apparatus or the like, the accurate actual surface temperature cannot be measured.
Thus, as regards a fixing device carrying out a fixing operation by controlling the temperature of the fixing roller within a specified temperature range to avoid the above-mentioned accident, it is disclosed a technology (refer to the Japanese publication of the unexamined patent application H7-13461, for example) to make it possible to carry out fixing always under a constant temperature distribution by it that, for example, with a structure such that a movable contact-type temperature sensor is brought into contact with the fixing roller to detect the surface temperature of the fixing roller during its stopping in warm-up, and during its rotation, the movable contact-type temperature sensor is retracted off the fixing roller, while a non-contact type temperature sensor detects the temperature of the fixing roller, the temperature difference between the surface temperature detected by the contact-type temperature sensor and the surface temperature detected by the non-contact type temperature sensor is obtained as a correction value, and by the addition of the above-mentioned correction value to the surface temperature detected by the non-contact type temperature sensor, the surface temperature of the fixing roller is detected, while the speed of the fixing roller is varied in accordance with the rising rate or falling rate of the detected surface temperature of the fixing roller.
However, this technology, although using a non-contact type temperature sensor, has a problem that the drive mechanism for retracting the movable contact-type sensor off the fixing roller when the fixing roller starts to rotate from the stopping state and varying the speed of the fixing roller in accordance with the rising rate and falling rate of the detected surface temperature of the fixing roller is complex, and also the control for driving the drive mechanism is complex.
Further, it is disclosed a technology (refer to the Japanese publication of the unexamined patent application 2001-242743) such that an appropriate temperature control of a fixing roller is practiced by it that a non-contact type temperature sensor is disposed in the neighborhood of the outer circumferential surface in the central part of a fixing roller, a contact-type temperature sensor being in contact with the outer circumferential surface is disposed at the end part of the fixing roller, in a state where the fixing roller is kept at a specified temperature, the temperature at the end part of the fixing roller is obtained by the contact-type temperature sensor, the temperature at the central part of the fixing roller is obtained by the non-contact type temperature sensor, and using this temperature difference as a correction value, by the addition of this correction value to the non-contact detection temperature at the central part detected by the non-contact temperature sensor, a corrected surface temperature approximating the actual surface temperature at the central part is obtained.
However, because this technology, although using a non-contact type temperature sensor, has a contact-type temperature sensor being in contact with the outer circumferential surface disposed at the end part of the fixing roller, there is a problem that, during the rotation of the fixing roller, or in the case of long term use, due to the friction in the contact area of the fixing roller and the contact type sensor, the fixing roller or the contact-type temperature sensor is damaged, or toner particles adhere to the contact part to make it impossible to detect an accurate temperature.
Therefore, it has been desired the development of an image forming apparatus equipped with a fixing device capable of detecting the temperature of the fixing roller without making the temperature sensor become in contact with the fixing roller, having a simple drive mechanism and a simple temperature control circuit for the fixing roller, and practicing a stable accurate temperature control of the fixing roller.
Further, this invention relates to an image forming apparatus having a fixing device of a heat roll method and a control method of said image forming apparatus.
(i) In a conventional fixing device of a heat roll method, for the control means of the surface temperature of the heating roller, it has been adopted means such that the surface temperature of the heating roller is measured by the use of a non-contact type temperature sensor in order to eliminate damages such as scratches on the coating layer of the heating roller surface, and the surface temperature of the heating roller is controlled on the basis of the measurement value.
In this case, as regards the actual temperature of the heating roller surface and the measured temperature by the temperature sensor which has measured the surface temperature of the heating roller, the measured temperature generally shows a temperature which is lower than the actual temperature by ΔT ° C.; therefore, it has been put into practice a temperature control of the heating roller surface such that a temperature which is lower than the surface temperature of the heating roller by ΔT ° C. is set as a control target temperature, which is compared with the measured temperature by the temperature sensor, and the difference is made to be zero (so as to make the surface temperature of the heating roller to become the target temperature as the result).
(ii) Further, it is disclosed a method in the Japanese publication of the unexamined patent application 2000-259033 a method in which the surface temperature of a fixing roller detected by a non-contact type surface temperature detection means is corrected by the detection of the surface temperature of the fixing roller using a contact-type surface temperature detection means being brought into contact with the fixing roller at a specified timing.
In the case of (i), between the temperature of the heating roller surface and the temperature by the temperature sensor for measuring the surface temperature of the heating roller, in the case where the surface temperature of the heating roller is varied, a temperature difference due to the time-lag of first order is produced on top of the temperature difference which is produced constantly.
For this reason, there is a defect that, near the end of warm-up for example, or even during printing, a large temperature difference between the two is produced during the heating of the heating roller, which causes the heating roller to be heated more than required, to raise a possibility that the heating roller is deteriorated or damaged, or an offset is produced.
In the case of (ii), although the above-mentioned defect is solved because the surface temperature of the fixing roller detected by a non-contact type surface temperature detection means is corrected by the detection of the surface temperature of the fixing roller using a contact-type surface temperature detection means to be brought into contact with the fixing roller, there is a defect that the fixing roller is possibly damaged because a contact-type surface temperature detection means is brought into contact with the fixing roller.
Heretofore, in a fixing device of a heat roll method, in practicing a control of the surface temperature of a heating roller, in order to eliminate scratches etc. on the coating layer of the heating roller surface, it has been adopted a method in which the surface temperature of a heating roller is measured by the use of a non-contact type detection sensor (a roller temperature detecting means), and the surface temperature of the heating roller is controlled on the basis of the measured value.
However, there is a problem that a non-contact type detection sensor has a slow response and its accuracy is low; as regards a method of solving this problem,                (iii) it is proposed a fixing device (the Japanese publication of the unexamined patent application 2001-215843) using a method in which the values of the surface temperature corresponding to a detection signal of an infrared ray receiving element (temperature detection sensor) of a non-contact type and a detection signal of a thermistor element (temperature compensation sensor) are used to compose a data table, and the detection output of the detection sensor and the detection output of the temperature compensation element are fitted to the data table, to correct the surface temperature of the fixing rotary body (heating roller) detected by the detection sensor.        
(iv) Further, it is proposed (Japanese publication of the unexamined patent application H5-289574) a fixing device in which a target design temperature (target control temperature) for controlling the temperature of a fixing roller (a heating roller) is calculated as a function of a time measurement value of the passage of the time from the turning-on of the power source measured by a timer, and the control of the surface temperature of the heating roller is carried out on the basis of the target control temperature which has been obtained from the result of the calculation.
In the case of (iii), a correspondence table of the surface temperature values TRn of the heating roller for the detection output values ERn of the detection sensor and the detection output values EHn of the compensation sensor as shown in FIG. 25 for example (a drawing of a data table for calculating surface temperature values on the basis of detection output values and compensation output values) is necessary; however, the fixing device has a defect that, in order to carry out a minute temperature control, it is necessary to prepare a large data table corresponding to various combinations of temperatures, a great deal of operation is required for the data preparation, and the data table requires a very large storage capacity.
In the case of (iv), because the surface temperature of a fixing roller is detected by a non-contact type sensor only, the device has a defect that the detection sensor of a non-contact type is subject to the influence of the ambient temperature and the condition of operation of the device, which makes it impossible to detect the correct surface temperature, and as the result, the target control temperature which is the calculation result for the correction of the surface temperature does not take a correct value; therefore, the device has a defect that also the surface temperature of the heating roller to be controlled on the basis of the target control temperature tends to become inaccurate.
In order to eliminate such defects, it has been studied also a method in which a detection sensor for detecting the temperature of a heating roller and a correction sensor for it are provided, and as shown in FIG. 26 for example (an illustrative drawing of calculation of a surface temperature by a conventional single operation equation), a single operation equation 1 for calculating the surface temperature over the whole range of the roller temperature is defined, and the surface temperature is calculated from the operation equation 1 on the basis of the output of the detection sensor and the output of the correction sensor, but it has been found that this method has a defect that the difference between the actual temperature and the result of calculation is large.
Further, this invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and a complex machine of these, and in particular, to an abnormal temperature detecting device of a fixing device.
Generally speaking, in an image forming apparatus of an electrophotographic method, an image is read by a scanner, a toner image of the read image is produced on a recording material in the image forming part, the recording material having the image formed is sent to a fixing device, where the unfixed toner image on the recording material is fixed by heating, and a print image is obtained.
The fixing device is equipped with a heating roller as a heating member equipped with a heating source inside, and a pressing roller as a pressing member making a pressure contact with said heating roller to form a fixing nip. The heating roller is driven for rotation by a drive source and the pressing roller is rotated in compliance with the heating roller. The heating roller and the pressing roller heat and press a recording material while they grip it to convey by the fixing nip, and fuse to fix a toner image on the recording material. As regards the heating roller, its surface temperature is detected and a temperature control is carried out to keep the temperature always proper.
Heretofore, for the temperature detection of the heating roller, it has been used a contact temperature detection method in which a temperature sensor such as a thermistor is brought into contact with the surface of a heating roller, to detect its surface temperature by the output of said temperature sensor. However, in a contact temperature detection method, because a temperature sensor is brought into a direct contact with the heating roller, it sometimes happens that the heating roller is damaged.
Therefore, in recent years, non-contact type temperature detecting devices which carry out the detection without being in contact with the heating roller have been proposed. As one of such non-contact type temperature detecting devices, it is known a detecting device equipped with a detection temperature sensor for detecting the temperature of the heating roller, and in addition to it, a compensation temperature sensor for the compensation of the detection temperature sensor for detecting the ambient temperature in the neighborhood of the detection temperature sensor.
As a method of detecting an abnormality of the temperature of a fixing device using such a temperature detecting device, for example, a method described in the Japanese publication of the unexamined patent application 2002-372892 is known.
However, because a fixing device is a high-temperature part, it is necessary to detect an abnormality of its temperature more closely and accurately.
As described in the above, it is the first object of this invention to provide a fixing device for use in an image forming apparatus in which a temperature detecting device which detects the surface temperature of a heating roller as a measurement object from the correlation between two different temperatures, a temperature detected by a surface temperature detection sensor for detecting the temperature mainly by heat radiation and a temperature detected by a compensation temperature sensor for detecting the ambient temperature mainly by heat conduction in air is made to accurately detect the surface temperature of said heating roller, with the conditions of its material and its placement position with respect to the above-mentioned heating roller established without breaking the relationship of said correlation.
It is the second object of this invention, in view of the above-mentioned problems, to provide an image forming apparatus equipped with a fixing device capable of practicing a stable accurate temperature control of the fixing roller.
It is the third object of this invention to provide an image forming apparatus which never produces the breakage of the heating roller or a fixing abnormality such as an offset by quickly detecting the surface temperature of the heating roller.
It is the fourth object of this invention to provide an image forming apparatus which does not require a large number of working hours for data preparation and a large storage capacity for data storage and is capable of quickly detecting the surface temperature of the heating roller and practicing the control without producing a breakage of the heating roller or a fixing abnormality such as an offset.
It is the fifth object of this invention to provide an abnormal temperature detecting device of a fixing device and an image forming apparatus capable of detecting abnormal temperatures minutely over a broader range in diversified ways.
The above-mentioned first object can be accomplished by any one of the following structures (1) to (4).
(1) A fixing device of an image forming apparatus having a heating roller provided with a heating means for heating a toner image formed on a transfer material and a temperature detecting device placed in a non-contact way with said heating roller, characterized by said temperature detecting device comprising a surface temperature detecting sensor for detecting the temperature of the surface of said heating roller, a compensation temperature sensor for detecting the ambient temperature, said surface temperature detecting sensor being placed at a first position in a case having an opening portion to which the heat radiation of said heating roller is directly incident through said opening and said compensation temperature sensor being enclosed by said case and placed at a second position to which the heat radiation of said heating roller is not directly incident, and means for calculating the surface temperature of said heating roller on the basis of the outputs of said two sensors, and said opening portion of said case for said surface temperature detecting sensor being disposed in such a way as not to enter a region between the vertical plane containing the central axis of said heating roller and the nearer one of two tangential planes to the circumferential surface of said heating roller parallel to said vertical plane.
(2) A fixing device of an image forming apparatus as set forth in the structure (1), characterized in that each angle made by each straight line drawn from the central position of each of the aforesaid two sensors perpendicularly to the central axis of the aforesaid heating roller, which represents the shortest distance between the central position and the central axis, and a plane containing the sensor surface of the corresponding one of said two sensors is 90 degrees±5 degrees.
(3) A fixing device of an image forming apparatus as set forth in the structure (1) or (2) characterized by the aforesaid case for accommodating the aforesaid two sensors of the aforesaid temperature detecting device and a mounting member to be attached to said case being made of a material having a good thermal conductivity.
(4) A fixing device of an image forming apparatus as set forth in any one of the structures (1) to (3), characterized by the aforesaid two sensors being fitted in such a way as to be covered by the part of said case excluding the aforesaid opening portion.
In order to accomplish the above-mentioned second object, as set forth in the structures (5) and (6) of this invention, in a state where a non-contact type temperature sensor was used and the fixing roller was standing still or rotating, investigations were repeatedly carried out in various ways in order that the temperature sensor placed at a position off the fixing roller may detect the temperature of the fixing roller accurately; then, it was found that the degree of the influence of the infrared rays, heat convection, etc. given to the temperature sensor in the environment where the fixing roller was arranged became different between two conditions of the fixing roller still standing and rotating, and it was also found that a higher temperature than the actual temperature of the fixing roller was detected in the condition of the rotating fixing roller because of the higher degree of the influence of heat given to the temperature sensor.
Further, it was found that, also during the rotation of the fixing roller, the degree of the above-mentioned influence of the heat convection etc. given to the temperature sensor, depending on the difference of the number of rotations, was higher for the higher number of rotations than for the lower number of rotations; therefore, correction values which became different dependently on the number of rotations were obtained by experiments etc., and by the practice of the temperature control of the fixing roller, in which the reference temperature of the temperature control means was set at a temperature obtained by the addition of the correction value to the set temperature of the fixing roller in order to correct the temperature difference, it was actualized to make it possible to keep the temperature of the fixing roller constant irrespectively of the number of rotations of the fixing roller.
That is, the invention set forth in the structure (5) is as follows.
(5) An image forming apparatus equipped with a fixing roller having a heater means inside for fixing a toner image formed on the basis of image information to a recording material, a temperature detecting means for detecting the temperature of said fixing roller in a condition of non-contact with said fixing roller and outputting the detection value of said temperature, and a temperature control means for practicing a temperature control of said fixing roller by making said heater means operate in such a way as to make said fixing roller come to be at a set temperature determined beforehand, on the basis of a reference temperature set beforehand and said detection value of said temperature, characterized by said temperature control means practicing a temperature control of said fixing roller, with said reference temperature during the rotation of said fixing roller made to have a temperature value obtained by the addition of a correction value α set beforehand to the set temperature value of said fixing roller.
By this structure, because a reference temperature having it taken into consideration that the temperature detecting means is subject to the influence of the turbulence of the rising convection heat flow produced by the rotation of the fixing roller during the rotation of the fixing roller is set in the temperature control means, it is possible to provide an image forming apparatus which is capable of keeping the surface temperature of the fixing roller always constant at the set temperature during the rotation of the fixing roller, and forming a high-quality image without producing a poor fixing etc.
(6) An image forming apparatus as set forth in the structure (5), characterized by the aforesaid temperature control means practicing the temperature control of the aforesaid fixing roller, when said fixing roller is rotating at a number of rotations smaller than the number of rotations of said fixing roller at the time the aforesaid reference temperature is made to have the temperature value obtained by the addition of the aforesaid correction value α to the set temperature value of said fixing roller, with said reference temperature made to have a value obtained by the addition of a correction value β set beforehand which is smaller than said correction value α to the set temperature value of said fixing roller.
By this structure, even in the case where the number of rotations of the fixing roller is changed, the surface temperature of the fixing roller is always kept constant during the rotation of the fixing roller irrespectively of the number of rotations of the fixing roller; thus, it is possible to provide an image forming apparatus capable of forming a high-quality image without producing a poor fixing etc.
The third object of this invention can be accomplished by any one of the structures (7) to (10) described below.
(7) An image forming apparatus equipped with a heating roller heated by a heat generating body, a roller heat detecting sensor for detecting the heat radiated from said heating roller, an ambient temperature detecting sensor for detecting the ambient temperature of said roller heat detecting sensor, a surface temperature calculating means for calculating the surface temperature information of said heating roller, and a heating control means for controlling the heating of said heating roller on the basis of the surface temperature information calculated by said surface temperature calculating means, characterized by said surface temperature calculating means calculating the surface temperature information of said heating roller by bringing the detection information of said roller heat detecting sensor and the detection information of said ambient temperature detecting sensor into correspondence with data table information in which the surface temperature information of the heating roller corresponding to the detection information of the roller heat detecting sensor and the detection information of the ambient temperature detecting sensor is written, and calculating the average value of the plural values of said surface temperature information calculated.
(8) A control method of an image forming apparatus characterized in that the moving average value of detection information obtained by a roller heat detecting sensor for detecting the heat radiated from a heating roller heated by a heat generating body and the moving average value of detection information obtained by an ambient temperature detecting sensor for detecting the ambient temperature of said roller heat detecting sensor are calculated, the surface temperature information of the heating roller corresponding to both the calculated moving average values is calculated from a data table in which the surface temperature information of the heating roller corresponding to the detection information of the roller heat detecting sensor and the detection information of the ambient temperature detecting sensor is written, the average value of the values of the calculated surface temperature information is calculated and is determined to be the roller surface temperature, which is compared with the fixing roller target temperature, and the temperature control of said heating roller is carried out on the basis of the result of the comparison.
(9) An image forming apparatus equipped with a heating roller heated by a heat generating body, a roller heat detecting sensor for detecting the heat radiated from said heating roller, an ambient temperature detecting sensor for detecting the ambient temperature of said roller heat detecting sensor, a surface temperature calculating means for calculating the surface temperature of said heating roller, and a heating control means for controlling the heating of said heating roller on the basis of the surface temperature information calculated by said surface temperature calculating means, characterized by further comprising a difference calculating means for calculating the difference between the detection information of said roller heat detecting sensor and the detection information of said ambient temperature detecting sensor, and said surface temperature calculating means calculating the surface temperature of said heating roller by bringing the output information of said difference calculating means and the detection information of said ambient temperature detecting sensor into correspondence with data table information in which the surface temperature information of the heating roller corresponding to the output information of the difference calculating means and the detection information of the ambient temperature detecting sensor is written, and calculating the average value of the plural values of said surface temperature information calculated.
(10) A control method of an image forming apparatus characterized by it that, by a difference calculating means for calculating the difference between output information obtained by a roller heat detecting sensor for detecting the heat radiated from a heating roller heated by a heat generating body and output information obtained by an ambient temperature detecting sensor for detecting the ambient temperature of said roller heat detecting sensor, the difference of the output information between both the sensors is calculated, the moving average value of the output information of said difference calculating means and the moving average of the detection information of said ambient temperature detecting sensor are calculated, the surface temperature information of the heating roller corresponding to both the calculated moving average values is calculated from a data table in which the surface temperature information of the heating roller corresponding to the output information of the difference calculating means and the detection information of the ambient temperature detecting sensor is written, the average value of the values of the calculated surface temperature information is calculated and is determined to be the roller surface temperature, which is compared with the fixing roller target temperature, and the temperature control of said heating roller is carried out on the basis of the result of the comparison.
Further, the inventors of the present invention are willing to provide an image forming apparatus having a structure such that an operation equation for calculating the surface temperature in a temperature range requiring accuracy is provided, calculations are carried out on the basis of the output values of a detection sensor and a compensation sensor obtained from time to time, and the temperature control of a heating roller is carried out by the comparison between the calculated surface temperature of the heating roller and a target control temperature.
Further, as shown in FIG. 24 (a graph of the result of calculation of plural equations), for the purpose of raising the detection accuracy of temperature, a temperature range A requiring accuracy (a temperature range where the temperature control of a heating roller is to be practiced) is further divided into two parts, for example; then, it is found in a graph showing the result of calculation by operation equations prepared corresponding to the respective temperature ranges B and C obtained by the dividing that the lines representing the calculation result are not parallel and cross each other like lines b and c, and in this case, it is to be remarked that the calculation result of the smaller values is nearer to the line a of the actual surface temperature. Thus, in the case where the calculation of the surface temperature is carried out for the same temperature range by means of plural operation equations, the result having the smaller values should be made to be the surface temperature.
In the above description, “a temperature range where the temperature control of the heating roller is to be carried out” means a temperature range of 80° C. to 220° C. in terms of the surface temperature of the heating roller requiring a temperature control with a good accuracy (for example, ±2° C. to 3° C. of the target value) as in the standby time, printing time, energy-saving operation time, etc. except for the warm-up time, and “a roller temperature range where normal printing is carried out” means, for example, a temperature range of 160° C. to 200° C. in terms of the surface temperature of the heating roller as in the normal printing time; these are to be determined suitably by the specification of the image forming apparatus including the developer material.
The above-mentioned fourth object of this invention can be accomplished by any one of the structures (11) to (16) described below.
(11) An image forming apparatus equipped with a heating roller heated by a heating source, a detection sensor for detecting the surface temperature of said heating roller in a non-contact way, and a compensation sensor for detecting the temperature of said detection sensor, characterized by further comprising a storage means having stored an operation equation defined in correspondence with a region determined by the roller temperature range where normal printing is practiced, a calculation means for calculating the surface temperature of said heating roller by means of said operation equation, and a control means for practicing a control of the application of electric current to said heating source on the basis of the calculation result and a target control temperature.
(12) An image forming apparatus equipped with a heating roller heated by a heating source, a detection sensor for detecting the surface temperature of said heating roller in a non-contact way, and a compensation sensor for detecting the temperature of said detection sensor, characterized by a roller temperature range where a temperature control of the heating roller is to be practiced being undivided, or divided into two or more temperature ranges, the detection output range of said compensation sensor being undivided, or divided into two or more ranges, and said image forming apparatus further comprising a storage means having stored two or more operation equations defined in correspondence with two or more regions determined by the one roller temperature range or two or more divisional roller temperature ranges and the one detection range or two or more divisional detection ranges of the compensation sensor respectively, a selection means for selecting an operation equation corresponding to one of said regions including a target control temperature and the detection temperature of said compensation sensor, a calculation means for calculating the surface temperature of said heating roller by means of the selected operation equation on the basis of the detection output of said detection sensor and the detection output of said compensation sensor, and a control means for practicing a control of the application of electric current to said heating source on the basis of the calculation result and the target control temperature.
(13) An image forming apparatus equipped with a heating roller heated by a heating source, a detection sensor for detecting the surface temperature of said heating roller in a non-contact way, and a compensation sensor for detecting the temperature of said detection sensor, characterized by a roller temperature range where a temperature control of the heating roller is to be practiced being divided into two or more temperature ranges, the detection output range of said compensation sensor being undivided, or divided into two or more ranges, and said image forming apparatus further comprising a storage means having stored operation equations defined in correspondence with regions determined by the divisional roller temperature ranges and the one detection range or two or more divisional detection ranges of the compensation sensor respectively, a calculation means for calculating the surface temperature of said heating roller by means of said defined plural operation equations on the basis of the detection output of said detection sensor and the detection output of said compensation sensor, a comparison judgement means for determining one having the smaller value to be a final surface temperature out of the plural calculation results, and a control means for practicing a control of the application of electric current to said heating source on the basis of said final surface temperature and a target control temperature.
(14) A control method of an image forming apparatus characterized by it that a detection output of a detection sensor for detecting the temperature of a heating roller and a detection output of a compensation sensor for detecting the temperature of said detection sensor are read, an operation equation stored beforehand for calculating the surface temperature of said heating roller set within a roller temperature range where normal printing is practiced is read, a calculation by said operation equation is carried out in accordance with the detection output of said detection sensor and the detection output of said compensation sensor, the calculation result is determined to be the surface temperature of said heating roller, which is compared with a target temperature, and a temperature control of said heating roller is practiced on the basis of the result of the comparison.
(15) A control method of an image forming apparatus characterized by it that a detection output of a detection sensor for detecting the temperature of a heating roller and a detection output of a compensation sensor for detecting the temperature of said detection sensor are read, a plurality of operation equations stored beforehand for calculating the surface temperature of said heating roller set within a temperature range where a temperature control of the heating roller is to be carried out are read, an operation equation corresponding to a target control temperature and the detection value of the compensation sensor is selected out of the read operation equations, a calculation by said selected operation equation is carried out in accordance with the detection output of said detection sensor and the detection output of said compensation sensor, the calculation result is determined to be the surface temperature of said heating roller, which is compared with a target temperature, and a temperature control of said heating roller is practiced on the basis of the result of the comparison.
(16) A control method of an image forming apparatus characterized by it that a detection output of a detection sensor for detecting the temperature of a heating roller and a detection output of a compensation sensor for detecting the temperature of said detection sensor are read, a plurality of operation equations stored beforehand for calculating the surface temperature of said heating roller set within a temperature range where a temperature control of the heating roller is to be carried out are read, a plurality of operation equations corresponding to the detection values of the compensation sensor are selected out of the read operation equations, a calculation by said selected operation equations is carried out in accordance with the detection output of said detection sensor and the detection output of said compensation sensor, the smallest one out of the calculation results is determined to be the surface temperature of said heating roller, which is compared with a target temperature, and a temperature control of said heating roller is practiced on the basis of the result of the comparison.
The above-mentioned fifth object of this invention can be accomplished by any one of the structures (17) to (28) described below.
(17) An abnormal temperature detecting device of a fixing device of an image forming apparatus for heating and fixing a toner image formed on a transfer material by a heating roller heated by a heating means, characterized by comprising a temperature detecting means having a first temperature sensor for detecting the surface temperature of said heating roller and a second temperature sensor for detecting the ambient temperature of said first temperature sensor, a comparison means for comparing a detection signal value of said first temperature sensor with a reference value set beforehand, and a judgement means for judging a temperature abnormality of said heating roller or an abnormality of said first temperature sensor from the comparison result of said comparison means.
According to the invention described in the structure (17), the abnormal temperature detecting device has a first temperature sensor for detecting the surface temperature of the heating roller and a second temperature sensor for detecting the ambient temperature of the first temperature sensor, compares a detection signal value of the first temperature sensor with a reference value set beforehand, and judges a temperature abnormality of the heating roller or an abnormality of the first temperature sensor. Accordingly, even if the second temperature sensor is not used, a temperature abnormality of the heating roller or an abnormality of the first temperature sensor can be detected.
(18) An abnormal temperature detecting device as set forth in the structure (17), characterized by the aforesaid judgement means judging the temperature to be abnormal in the case where a state that the detection signal value of the aforesaid first temperature sensor does not exceed the aforesaid reference value set beforehand lasts for a period of time not shorter than a reference time set beforehand as the result of the aforesaid comparison.
(18) According to the invention described in the structure (18), in the invention of the structure (17), the abnormal temperature detecting device judges the temperature to be abnormal in the case where a state that the detection signal value of the aforesaid first temperature sensor does not exceed the aforesaid reference value set beforehand lasts for a period of time not shorter than a reference time set beforehand. Accordingly, it is possible to detect a temperature abnormality of the heating roller or an abnormality of the first temperature sensor more accurately.
(19) An abnormal temperature detecting device of a fixing device of an image forming apparatus for heating and fixing a toner image formed on a transfer material by a heating roller heated by a heating means, characterized by comprising a temperature detecting means having a first temperature sensor for detecting the surface temperature of said heating roller and a second temperature sensor for detecting the ambient temperature of said first temperature sensor, a differential amplification means for differentially amplifying a detection signal value of said first temperature sensor and a detection signal of said second temperature sensor to obtain the difference value, and a judgement means which judges the temperature to be abnormal in the case where a state that the difference value does not exceed a reference value set beforehand lasts for a period of time not shorter than a reference time set beforehand.
According to the invention described in the structure (19), the abnormal temperature detecting device comprises a first temperature sensor for detecting the surface temperature of said heating roller and a second temperature sensor for detecting the ambient temperature of said first temperature sensor, differentially amplifies a detection signal value of said first temperature sensor and a detection signal of said second temperature sensor to obtain the difference value, and judges the temperature to be abnormal in the case where a state that the difference value does not exceed a reference value set beforehand lasts for a period of time not shorter than a reference time set beforehand. Accordingly, it is possible to detect an abnormality concerning the heating roller or the two sensors.
(20) An abnormal temperature detecting device of a fixing device of an image forming apparatus for heating and fixing a toner image formed on a transfer material by a heating roller heated by a heating means, characterized by comprising a temperature detecting means having a first temperature sensor for detecting the surface temperature of said heating roller and a second temperature sensor for detecting the ambient temperature of said first temperature sensor, a differential amplification means for differentially amplifying a detection signal value of said first temperature sensor and a detection signal of said second temperature sensor to obtain the difference value, and a judgement means which judges the temperature to be abnormal in the case where a state that the detection signal of the first temperature sensor does not exceed a first reference value set beforehand lasts for a period of time not shorter than a first reference time set beforehand, in the case where a state that the detection signal of the second temperature sensor does not exceed a second reference value set beforehand lasts for a period of time not shorter than a second reference time set beforehand, or in the case where a state that the difference value does not exceed a third reference value set beforehand lasts for a period of time not shorter than a third reference time set beforehand.
According to the invention described in the structure (20), the abnormal temperature detecting device comprises a first temperature sensor for detecting the surface temperature of said heating roller and a second temperature sensor for detecting the ambient temperature of said first temperature sensor, differentially amplifies a detection signal value of said first temperature sensor and a detection signal of said second temperature sensor to obtain the difference value, and judges the temperature to be abnormal in the case where a state that a detection signal of the first temperature sensor does not exceed a first reference value set beforehand lasts for a period of time not shorter than a first reference time set beforehand, in the case where a state that a detection signal of the second temperature sensor does not exceed a second reference value set beforehand lasts for a period of time not shorter than a second reference time set beforehand, or in the case where a state that the difference value does not exceed a third reference value set beforehand lasts for a period of time not shorter than a third reference time set beforehand. Accordingly, because an abnormality is detected by the use of outputs from the two sensors and the difference value of outputs of the two sensors, it is possible to detect an abnormality more accurately.
(21) An abnormal temperature detecting means as set forth in the structure (20), characterized by it that with the aforesaid first reference time denoted by t1, the aforesaid second reference time denoted by t2, and the aforesaid third reference time denoted by t3, these reference times are set in such a way as to satisfy the inequality t1<t2<t3.
According to the invention described in the structure (21), in the invention described in the structure (20), with the aforesaid first reference time denoted by t1, the aforesaid second reference time denoted by t2, and the aforesaid third reference time denoted by t3, these reference times are set in such a way as to satisfy the inequality t1<t2<t3. Accordingly, it is possible to carry out the abnormality judgement in the order of importance as the abnormality detection.
(22) An abnormal temperature detecting device of a fixing device of an image forming apparatus for heating and fixing a toner image formed on a transfer material by a heating roller heated by a heating means, characterized by comprising a temperature detecting means having a first temperature sensor for detecting the surface temperature of said heating roller and a second temperature sensor for detecting the ambient temperature of said first temperature sensor, a differential amplification means for differentially amplifying a detection signal value of said first temperature sensor and a detection signal of said second temperature sensor to obtain the difference value, a positive-and-negative source voltage supply means for supplying a positive source voltage and a negative source voltage for making the operation region of said differential amplification means cover a range extending from a negative voltage to a positive voltage to said differential amplification means, and a judgement means which judges the temperature to be abnormal in the case where the signal polarity of said difference value is negative.
According to the invention described in the structure (22), the abnormal temperature detecting device comprises a temperature detecting means having a first temperature sensor for detecting the surface temperature of said heating roller and a second temperature sensor for detecting the ambient temperature of said first temperature sensor, differentially amplifies a detection signal of said first temperature sensor and a detection signal of said second temperature sensor to obtain the difference value, and judges the temperature to be abnormal in the case where the signal polarity of the difference value is negative. Accordingly, it is possible to detect an abnormality in the abnormal temperature detecting device such as an abnormality of the temperature of the heating roller, the two sensors, the circuit structure.
(23) An abnormal temperature detecting device as set forth in the structure (22), characterized by the aforesaid judgement means judging the temperature to be abnormal in the case where a state that the signal polarity of the aforesaid difference value is negative lasts for a period of time not shorter than a reference time determined beforehand.
According to the invention described in the structure (23), in the invention described in the structure (22), the judgement means judges the temperature to be abnormal in the case where a state that the signal polarity of the aforesaid difference value is negative lasts for a period of time not shorter than a reference time determined beforehand. Accordingly, it is possible to detect an abnormality more certainly.
(24) An abnormal temperature detecting device as set forth in any one of the structures (17) to (23), characterized by further comprising a control means which, in the case where the result of the judgement by the aforesaid judgement means indicates an abnormality, once stops the operation of the aforesaid heating means and later actuates it again and if said judgement means judges the temperature to be abnormal again, judges the temperature to be abnormal.
According to the invention described in the structure (24), in the invention described in any one of the structures (17) to (23), in the case where the result of the judgement by the judgement means indicates an abnormality, the control means once stops the operation of the heating means and later actuates it again, and if the judgement means judges the temperature to be abnormal again, judges the temperature to be abnormal. Accordingly, it is possible to detect whether an abnormality is true or false more certainly.
(25) An abnormal temperature detecting device as set forth in any one of the structures (17) to (23), characterized by the aforesaid temperature detecting means includes a third temperature sensor placed at another position different from the placement position of the aforesaid first temperature sensor for detecting the surface temperature at the another position of the aforesaid heating roller, and said abnormal temperature detecting device further comprising a confirmation means for confirming an abnormality on the basis of a detection signal value of said third temperature sensor and a third reference value set beforehand.
According to the invention described in the structure (25), in the invention described in any one of the structures (17) to (23), the abnormal temperature detecting device has a third temperature sensor placed at another position different from the placement position of the aforesaid first temperature sensor for detecting the surface temperature at the another position of the aforesaid heating roller, and confirms an abnormality on the basis of a detection signal value of said third temperature sensor and a third reference value set beforehand, in the case where the result of the judgement by the judgement means indicates an abnormality. Accordingly, it is possible to detect whether an abnormality is true or false more certainly.
(26) An abnormal temperature detecting device as set forth in the structure (25), characterized by further comprising a control means which, in the case where the result of the confirmation by the aforesaid confirmation means indicates an abnormality, once stops the operation of the aforesaid heating means and later actuates it again and if said judgement means judges the temperature to be abnormal again, judges the temperature to be abnormal.
According to the invention described in the structure (26), in the invention described in the structure (25), in the case where the result of the confirmation by the aforesaid confirmation means indicates an abnormality, the control means once stops the operation of the aforesaid heating means and later actuates it again and if said judgement means judges the temperature to be abnormal again, judges the temperature to be abnormal. Accordingly, it is possible to detect whether an abnormality is true or false more certainly.
(27) An abnormal temperature detecting device as set forth in any one of the structures (18) to (21), and (23), characterized by further comprising a switching means for changing the length of the reference time set in the aforesaid judgement means.
According to the invention described in the structure (27), in the invention described in the structures (18) to (21), and (23), the abnormal temperature detecting device further comprises a switching means for changing the length of the reference time set in the aforesaid judgement means. Accordingly, in the case where a uniformly determined reference time results in the damage of the fixing device, for example, in the case where there are different destination lands, it is possible to set different reference times in accordance with the conditions.
(28) An image forming apparatus characterized by being equipped with an abnormal temperature detecting device of a fixing device as set forth in any one of the structures (17) to (27).
According to the invention described in the structure (28), by being equipped with an abnormal temperature detecting device of a fixing device as set forth in any one of the structures (17) to (27), the image forming apparatus can detect a temperature abnormality minutely over a broad range in diversified ways.